Cornea

These are the layers of the cornea - each with different functions and capabilities.

Layers of the cornea
  1. Epithelium: As the cornea's outermost region--comprising about 10 percent of the tissue's thickness--the epithelium functions primarily to:
    • block the passage of foreign material - such as dust or water - into the eye and other layers of the cornea, and
    • provide a smooth surface that absorbs oxygen and other needed cell nutrients that are contained in tears.
    This layer, which is about five cells deep, is filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched.
  2. Bowman's Layer lies between the epithelium and the stroma. It is comprised of strong collagen fibers and helps the cornea keep its shape.
  3. Stroma: Located behind the epithelium, the stroma comprises about 90 percent of the cornea. It consists primarily of water (78 percent); layered protein fibers (16 percent) that give the cornea its strength, elasticity, and form; and cells that nourish it. The unique shape, arrangement, and spacing of the protein fibers are essential in producing the cornea's light-conducting transparency.
  4. Dua's Layer is a very thin layer of collagen which is impervious to air.
  5. Descemet's membrane lies between the stroma and endothelium layer. The endothelium cells grow upon it and if it is damaged, they cannot grow.
  6. Endothelium: This single layer of cells is located between the stroma and the aqueous humor. Because the stroma tends to absorb water, the endothelium's primary task is to pump excess water out of the stroma. Without this pumping action, the stroma would swell with water, become hazy, and ultimately opaque.

Related diseases: Fuch's Dystrophy.